Cosmianthemum melinhense D.V.Hai, Z.L.Lin & Y.F.Deng, 2022

Hai, Do Van, Cuong, Nguyen The, Choudhary, Ritesh Kumar, Lin, Zheli & Deng, Yunfei, 2022, Cosmianthemum melinhense (Acanthaceae), a new species from the Me Linh Station for Biodiversity in northeastern Vietnam, Phytotaxa 538 (2), pp. 124-132 : 125-129

Cosmianthemum melinhense D.V.Hai, Z.L.Lin & Y.F.Deng , sp. nov. ( Figs. 2–4 )

Type: — VIETNAM. Vinh Phuc Province: Phuc Yen Town, Ngoc Thanh commune, elev. ca. 152 m, 21°23’51.3”N, 105°42’56.8”E, 21 October 2016, Do Van Hai, Trinh Xuan Thanh, DVH 149 (holotype HN!; isotypes HN!, IBSC!) .

Herbs 0.3–0.6 m tall. Stems subterete, swollen at nodes, pubescent when young, soon glabrescent. Leaves opposite; petiole 12–15 mm long, pubescent; blade elliptic to ovate, lanceolate, 12–16 × 4–6 cm, adaxially dark green, glabrous, abaxially light green, pubescent along the veins, densely punctate with grayish white strip-like cystoliths, secondary veins 6–8 on each side of midvein, one pair of veins near base, midvein and secondary veins abaxially prominent, base cuneate to attenuate, margin entire to subsinuate, with marginal gland, apex acute to shortly acuminate. Inflorescence compound dichasia in terminal or axillary, the axis glandular, 7–10 cm long, interrupted, usually in a leafy thyrse, peduncle 0.5–1.5 cm long; cymes 3–9-flowered; bracts subulate, 4–5 × 1–1.3 mm, basal ones longer, then gradually smaller with apical most ones, outside pubescent, with sparely gland-tipped pubescence, apex acute; bracteoles subulate, 2.5–3.5 × 0.8–1.3 mm, outside pubescent with sparely gland-tipped pubescence, apex acute. Calyx ca. 6 mm long, 5-lobed; lobes linear-lanceolate, ca. 4 × 0.5–0.8 mm, subequal, apex acuminate, outside sparsely glandtipped pubescent; inside densely gland-tipped pubescent. Corolla green-purple, 1.4–1.5 cm long, outside gland-tipped pubescent; tube basally cylindric and 1.5–2 mm wide for 4.5–5 mm long; limb strongly 2-lipped, lower lip violet dotted, 5–5.5 mm broad, 3-lobed, middle lobes bigger than laterals, middle ovate, ca. 2.5 mm long, laterals oblong, 1– 1.5 × 2 mm; upper lip violet blotched, triangular, ca. 6 × 6 mm, 2-cleft. Stamens 2, exserted; filaments ca. 6 mm long, glabrous; anthers bithecous, thecae oblong, ca. 2.5 mm long, superposed, muticous at base; staminodes 2, linear, 2–2.5 mm long, glabrous. Ovary glabrous, green, fusiform with nectary flower disc bowl-shaped at base; style 9–10 mm long, glabrous, stigma slightly 2-lobed. Capsule clavate, 2.5–2.8 cm long, sterile portion 1.2–1.6 cm long, puberulent. Seeds 4, ca. 3.5 × 5 mm, ovate, scarcely compressed, pale brown, rugulose-alveolate.

Etymology: —The species is named after the type locality, Me Linh Station for Biodiversity in Vinh Phuc Province, northeastern Vietnam.

Phenology: —It was observed in flowering from October to January and fruiting from December to April.

Distribution and ecology: — Cosmianthemum melinhense is currently known from Ngoc Thanh Commune, Phuc Yen Town, Vinh Phuc Province, and probably endemic to the northern region of Vietnam. It grows under the shades in secondary evergreen broad-leaved forest in association with bamboos, along the streams at elevation of about 150 m. The associated plants include Bauhinia khasiana Baker (1878: 281) , Christella dentata (Forssk.) Brownsey & Jermy (1973: 338) , Melicope pteleifolia (Champ. ex Benth.) T.G. Hartley (1993: 521) , Pteris grevilleana Wall. ex J. Agardh (1839: 23) , Pronephrium triphyllum (Sw.) Holttum (1972: 122) , Strobilanthes mucronatoproducta Lindau (1897: 650) , etc.

Conservation status: — Cosmianthemum melinhense is known only from the type locality which lies within a protected area. During our investigation in this area, we could observe only a few scattered populations growing in secondary forests, along nature trail near streams. Because of its narrow distribution with an estimated population size of <1000 mature individuals, it is assessed to be Vulnerable (VU) following the IUCN Red List Categories and Criteria ( IUCN 2012, 2019). Further inventories are needed to find additional populations in Vietnam. The discovery of C. melinhense along with many new species tells more about the floristic richness and diversity of the Me Linh Station for Biodiversity, for which further studies are necessary in the future.

Additional Specimens Examined (Paratypes): — VIETNAM. Vinh Phuc: Phuc Yen Town, Ngoc Thanh commune, elev. ca. 57 m, 21°22’40.7”N, 105°42’41.3”E, 27 January 2013, Do Van Hai et al., ML281 (HN) ; ibid. elev. ca. 155 m, 21°23’51.7”N, 105°43’41.2”E, 25 January 2015, Do Van Hai et al., MLS 135 (HN) ; ibid. elev. ca. 160 m, 21°23’52.3”N, 105°42’56.3”E, 15 January 2018, Do Van Hai, DVH 15012018 (HN) ; ibid. elev. ca. 148 m, 21°23’48.9”N, 105°42’56.9”E, 24 March 2021, Do Van Hai, Nguyen The Cuong, Trinh Xuan Thanh, DVH 399 ( HN) .

Notes: — Cosmianthemum melinhense is allied to C. guangxiense H.S.Lo & D.Fang in Fang et al. (1997: 42), C. knoxiifolium and C. viriduliflorum (C.Y.Wu & H.S.Lo) H.S.Lo in Fang et al. (1997: 42) from China in the characters of the inflorescence, stamens, staminodes, and fruits. However, it differs from C. viriduliflorum in having elliptic to ovate, lanceolate leaf blade with more pairs of secondary veins, longer bracts and calyx, style, and fruits, and corolla with gland-tipped pubescence outside, style glabrous. However, C. viriduliflorum has pubescent corolla and style. It differs from C. guangxiense by its shorter habit, more pairs of secondary veins, subulate bracts, 4–5 × 1–1.3 mm, outside pubescent and sparely gland-tipped pubescent, longer petioles and calyx with lobes linear-lanceolate, ca. 6 mm long, outside sparsely gland-tipped pubescent. Furthermore, it differs from C. knoxiifolium by shorter petioles, pubescent, shorter inflorescence but longer bracts, calyx, corolla, staminodia and calyx outside sparsely gland-tipped pubescent. The detailed comparison among C. melinhense , C. guangxiense , C. knoxiifolium and C. viriduliflorum is given in Table 1 .

Figures

FIGURE 2. Cosmianthemum melinhense. A. Habitat, B. A branch of inflorescence, C. Bract, D. Bracteole, E. Calyx, F. Corolla (open), G. Stamens, H. Ovary and style, I. Fruit, J. Seed (Drawn by Mrs. Le Kim Chi).

FIGURE 3. Cosmianthemum melinhense. A. Habitat, B. A twig showing leaf characters, C, D. Leaf (abaxial and adaxial view) (Photos by Do Van Hai).

FIGURE 4. Cosmianthemum melinhense. A. Habitat, B. Inflorescence, C. A part of inflorescence, D. Calyx, E. Flowers in front view, F, G. Flower (rear and lateral view), H. Corolla (open), I. Stamens, J. Ovary and style, K. Fruit (closed), L. Fruit (open), M. Seed (Photos by Do Van Hai).